Conventional vinyl wallcoverings are often relatively impervious to moisture and can actually serve as an effective moisture barrier. While moisture impermeability can be desirable in many wallcovering applications, such as in bathrooms and kitchens, moisture impermeable wallcoverings can cause problems in extremely humid climates. Under conditions of high humidity, moist air can permeate the building walls from the exterior inwardly and condense between the wall and the wallcovering on account of the difference between the inside and outside temperature. The low moisture permeability of conventional vinyl wallcoverings prevents moisture and condensate from passing through into the room at a rate equal to the rate at which moisture permeates inwardly through the building walls, thereby causing accumulation of moisture at the side of the wallcovering facing the wall. The trapped water between the wallcovering and the wall provides an excellent medium for growth of molds and mildew on account of the presence of the wallcovering paste which generally contains organic materials which serve as nutrients for sustaining the growth of molds and mildew. Because of the ubiquitous nature of mold and mildew spores, it is almost inevitable that any accumulation of moisture at the interface between a wall and wallcovering will lead to the growth of molds or mildew. Such growth is generally accompanied by staining or discoloration of the wallcovering and by the presence of offensive odors. Conventional vinyl wallcoverings generally have a moisture permeability of about 1 or 2 Perms.
U.S. Pat. No. 5,262,444 to Rusincovitch et al. discloses a breathable, plastic film, useful as a wallcovering material, which is prepared by combining a plastisol with a low boiling point additive, extruding the plastisol mixture containing the low boiling point additive to form a film, and curing the film under conditions whereby the additive volatilizes through the cured film to form a multiplicity of holes in the film. The reference reports Perm values generally ranging from about 1.0 to about 20.0. While the Rusincovitch et al. patent generally reports Perm values which are considerably higher than those of conventional vinyl wallcoverings, still higher moisture permeabilities would be advantageous and desirable.
Pending U.S. patent application Ser. No. 08/013,911, filed Feb. 5, 1993, discloses a moisture-permeable acoustic lamina, suitable for use as a wallcovering, which comprises a woven fabric adhered to a fabric backing by a discontinuous thermoplastic polymer layer. The acoustic lamina is reported to achieve very high Perm values, such as about 72 Perms. The disclosed wallcoverings are particularly well suited for those situations where sound damping and moisture permeability are both important, but where a smooth aesthetic appearance is not desired or can be sacrificed in favor of the excellent moisture permeability and sound damping properties. Specifically, the outer layer of the acoustic lamina is a relatively coarse woven fabric which provides a rough textured surface needed for good sound damping properties. Because of the rough textured surface it is not possible, or at least impracticable, to provide the acoustic lamina of the referenced application with a distinct, sharply-defined printed design or pattern because the printing would tend to deposit more ink on the higher areas and completely miss the recessed areas of the exposed surface.
Accordingly, there exist a need for a breathable wallcovering having a relatively higher permeability, yet which has a smooth outer exposed surface which can be printed with a design or pattern having sharply defined edges.